DESCRIPTION: (Applicant's Abstract) The proposed research has as its two main goals the synthesis and testing of (1) cocaine antagonists targeted to the stimulant binding site on the dopamine uptake complex and (2) a bivalent GBR 12783 derivative to be used as a probe for the dopamine transporter. The cocaine antagonists to be synthesized are reversibly and irreversibly binding analogs of three stimulant agents (methylphenidate, GBR 12783 and LR 5182). It is hypothesized that structural modifications of these compounds will produce therapeutic agents which inhibit cocaine binding, but spare dopamine uptake. The synthesized compounds will be tested in rat striatal tissue in vitro for activity at the cocaine binding site using the [3H]WIN 35,428 radioreceptor assay and for ability to block synaptosomal [3H]dopamine transport. The ability to antagonize the behavioral effects of cocaine mediated through central dopaminergic pathways will be evaluated using tests which measure locomotor activity, cocaine discrimination and rotation following unilateral nigrostriatal lesions. Those derivatives demonstrating partial agonist or antagonist activity in the behavioral studies will be tested ex vivo in the [3H]WIN 35,428 and [3H]dopamine transport assays to better define their interaction with the dopamine uptake complex in vivo. If the bivalent GBR 12783 derivative exhibits activity at the dopamine transport complex, it will be tritiated by reduction of the olefinic bond. The radiolabeled compound will be used to characterized the dopamine transporter by means of one- and two dimensional gel electrophoresis. Successful completion of this work will result in drugs with therapeutic potential against the reinforcing and addicting properties of cocaine. It will also provide a unique radiolabeled probe which will allow the exploration of interrelated domains on the transporter, and, unlike photoaffinity labels, can be used for in vivo studies. Ultimately, this work could have a positive impact on our understanding of various disorders involving dopaminergic systems (e. g., Parkinson's disease, schizophrenia and Tourette's syndrome).